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Old Aug 21, 2011, 06:54 AM
Steamers & Military Ships
Bergen, Norway
Joined Jul 2007
45 Posts
Help!
How to get a PPM signal from old Futaba PCM radio?

I am helping out a friend. He has an old Futaba FP-T8H-P radio (non computer) which we woud like to convert to 2.4 GHz with a FrSky DIY module. The radio seems to be an earlier verson of this one: http://manuals.hobbico.com/fut/8sghp-manual.pdf. The FrSky module requires a PPM signal but this a PCM radio. There is no trainer connection, just a connection for a charger (only two wires on the inside), and I have not found any switches to change from PCM to PPM.

Does anyone know if it is possible to get at PPM signal out of this radio?

HelgeBe
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Last edited by HelgeBe; Aug 21, 2011 at 03:19 PM.
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Old Aug 21, 2011, 09:59 AM
Dave the Rave
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Joined Jun 2007
876 Posts
I could be wrong (if I am I'm sure somebody will correct me), but I think the type of signal being transmitted (PPM vs PCM) is determined by the circuitry in that RF module. If you replace it with something different, like a 2.4GHz PPM module, everything should work OK.

I've personally never seen a Futaba like that. Interesting collection of features.
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Old Aug 21, 2011, 11:16 AM
"Unnecessary Necessity"
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Canada, QC, Quebec City
Joined Sep 2006
5,888 Posts
The RF section has nothing to do with the encoder output (ppm/pcm), it just set the modulation type (AM/FM) and frequency band from 27 Mhz to 2.4 Ghz. The Tx in question has a DSC output combined with the charging jack (DIN-6)but that signal is most likely a digital number serie (PCM) instead of a pulse train with variable length like PPM. The best way would be to check that signal with a oscilloscope to determine if it is ppm or pcm. If it is PCM only you won't be able to convert that Tx.
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Old Aug 21, 2011, 11:33 AM
Registered User
Haifa, Israel
Joined Nov 2009
137 Posts
Try to check the signals that go into the RF module. You will need an oscilloscope or a logic analyzer for that. I'm pretty sure that you will find only a PCM signal but that is your best chance.

Edit:
Just seen coriolan's answer. I agree.
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Old Aug 21, 2011, 11:50 AM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
3,661 Posts
The slightly later FF7 transmitter had the facility to DSC with a receiver via the trainer socket but there was never any evidence that this signal was PCM. I believe it was CPPM a signal because I haven't come across any discussion of the PCM signal being available at the trainer socket, I would say it's likely to be the same on the 8SG, but you will need a scope to be certain.

A.
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Old Oct 16, 2011, 09:26 PM
Registered User
Chennai, India
Joined Oct 2004
10 Posts
Help

I have a similar problem. I have a FP-T4H transmitter (4 channel with 27 mHz am transmission) which I want to convert to 2.4gHz with a Assan X8D hack module. However, I have not been able to locate a PPM signal on the single board that is there.

Could some body help me in this. If it is not possible to get a ppm signal, I dont mind building up the ppm signal with my own board, but I will need help with a simple encoder circuit. The transmitter mechanism is in perfect condition and the pots are without jitter.

Saju
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Old Oct 17, 2011, 10:06 AM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
3,661 Posts
An oscilloscope is the best way to find a PPM signal if it exists, without one you are effectively blindfolded from an electronic point of view.

A.
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